1. Field of the Invention
The present invention relates to a signal detection method and a device of a data recording/reproducing apparatus and, more particularly, to a signal detection method and device of a data recording/reproducing apparatus, by which data reproduced from a data recording/reproducing apparatus is processed such that the data recorded in the data recording/reproducing apparatus can be detected exactly.
2. Description of the Related Art
In this information age, much research has been conducted in a high-speed and high-capacity data storage devices for easily storing and using massive amounts of data.
In general, signals passed through an optical recording/reproducing apparatus interfere with each other, as data is recorded with a high density, making signal detection difficult. Such interference is linearly modeled in an optical recording/reproducing apparatus, in this respect which is similar to a magnetic recording/reproducing apparatus.
However, because high frequency light is scattered greatly by reflection when detecting signals, not at all the high frequency light cannot reach a detector. Thus, the spectral density of signals with respect to frequency in the optical recording/reproducing apparatus is more rapidly decreased than in the magnetic recording/reproducing apparatus. Thus, the optical recording/reproducing apparatus may be a linear system for passing only low frequency signals. Also, the average DC value as a reference for (+)/(-) signal detection is riot stable in this state, so the signal becomes unstable. In order to detect signals by overcoming such phenomena, an eight-to-fourteen modulation-plus (EFM-plus) code is used for recording data, and a suitable equalizer and detector are used for reading the data. The equalizer corrects the signals distorted by mutual interference to make the signal detection easy. The detector properly classifies the signals passed through the equalizer into +1 or -1. In particular, an optical recording/reproducing channel has a null frequency shorter than a rate 1/2T, so that it is unfavorable to detect data by completely removing intersymbol interference (ISI). That is, it is favorable to leave some degree of constructive ISI which is helpful for detection. However, a detection method using a minimum mean square error (MMSE) linear equalizer and a threshold detector completely removes ISI, thereby amplifying noise, and as a result, the performance of an apparatus is lower. Also, a decision feedback equalizer (DFE) is realized within the limits of the number of taps, so that removal of ISI is also limited, thereby leaving ISI. However, the remaining ISI is destructive for detection and badly affects a detector, thereby lowering performance. Also, a method using a partial response maximum likelihood (PRML) is not suitable for a target of a conventional (1+D).sup.n power/spectrum in which the null cycle is set to the channel having a cycle of 1/2T. Thus, the PRML method should establish another PR target.